Dual pipe

Abstract

A dual pipe includes an outer pipe having a valley/ridge portion on an outer circumferential surface thereof, and an inner pipe having a valley/ridge portion formed on an inner circumferential surface thereof and inserted into the outer pipe. In the dual pipe, the inner pipe and the outer pipe are threadedly engaged with each other. A low pressure refrigerant passes through the inner pipe. In order to secure a passage of a high pressure refrigerant in a space between the outer circumferential surface of the inner pipe and the inner circumferential surface of the outer pipe, a part of the helical valley/ridge portion formed on the outer circumferential surface of the inner pipe is composed of a multiple-helix helical valley/ridge portion.

What is claimed is: 
     
       1. A dual pipe, comprising:
 an inner pipe having a helical valley/ridge portion formed on an outer circumferential surface thereof; and 
 an outer pipe into which the inner pipe is inserted, 
 wherein the helical valley/ridge portion of the inner pipe includes a first helical inner pipe valley/ridge portion, a second helical inner pipe valley/ridge portion and a third helical inner pipe valley/ridge portion formed sequentially in a longitudinal direction to have the same pitch, the second helical inner pipe valley/ridge portion being a multiple-helix helical valley/ridge portion, 
 the inner pipe further includes a first annular groove formed by reducing an outer diameter of the inner pipe between the first helical inner pipe valley/ridge portion and the second helical inner pipe valley/ridge portion and a second annular groove formed by reducing an outer diameter of the inner pipe between the second helical inner pipe valley/ridge portion and the third helical inner pipe valley/ridge portion, 
 the outer pipe includes a first helical outer pipe valley/ridge portion, a second helical outer pipe valley/ridge portion and a third helical outer pipe valley/ridge portion formed on an inner circumferential surface of the outer pipe so as to be threadedly engaged with the first helical inner pipe valley/ridge portion, the second helical inner pipe valley/ridge portion and the third helical inner pipe valley/ridge portion, respectively, and 
 the outer pipe includes a first through-hole formed between the first helical outer pipe valley/ridge portion and the second helical outer pipe valley/ridge portion and a second through-hole formed between the second helical outer pipe valley/ridge portion and the third helical outer pipe valley/ridge portion. 
 
     
     
       2. The dual pipe according to  claim 1 , wherein the first helical outer pipe valley/ridge portion, the second helical outer pipe valley/ridge portion and the third helical outer pipe valley/ridge portion of the outer pipe are single-helix helical valley/ridge portions and are configured to extend integrally. 
     
     
       3. The dual pipe according to  claim 1 , wherein the first helical inner pipe valley/ridge portion and the third helical inner pipe valley/ridge portion of the inner pipe are multiple-helix helical valley/ridge portions,
 the first helical outer pipe valley/ridge portion and the third helical outer pipe valley/ridge portion of the outer pipe are multiple-helix helical valley/ridge portions, and 
 the second helical outer pipe valley/ridge portion is a single-helix helical valley/ridge portion. 
 
     
     
       4. The dual pipe according to  claim 1 , wherein the inner pipe includes a smaller-diameter connecting portion extending from the third helical inner pipe valley/ridge portion and having an outer circumferential surface diameter smaller than a diameter of an imaginary cylinder defined by an inner circumferential surface of a ridge of one of the first, second and third helical valley/ridge portion formed on the inner circumferential surface of the outer pipe,
 the outer pipe further includes a fixing portion extending from the third helical outer pipe valley/ridge portion, and 
 the dual pipe further comprises a seal ring inserted between the smaller-diameter connecting portion of the inner pipe and the fixing portion of the outer pipe. 
 
     
     
       5. The dual pipe according to  claim 1 , wherein the inner pipe includes a smaller-diameter connecting portion extending from the third helical inner pipe valley/ridge portion and having an outer circumferential surface diameter smaller than a diameter of an imaginary cylinder defined by an inner circumferential surface of a ridge of one of the first, second and third helical valley/ridge portions formed on the inner circumferential surface of the outer pipe, and
 the outer pipe further includes a fixing portion extending from the third helical outer pipe valley/ridge portion so that a fixing portion of the inner pipe is inserted into the fixing portion of the outer pipe. 
 
     
     
       6. The dual pipe according to  claim 1 , wherein the first helical inner pipe valley/ridge portion, the second helical inner pipe valley/ridge portion and the third helical inner pipe valley/ridge portion of the inner pipe are formed by pressing the outer circumferential surface of the inner pipe, and
 the first helical outer pipe valley/ridge portion, the second helical outer pipe valley/ridge portion and the third helical outer pipe valley/ridge portion of the outer pipe are formed by pressing the outer circumferential surface of the outer pipe. 
 
     
     
       7. A dual pipe, comprising:
 an inner pipe having a helical valley/ridge portion formed on an outer circumferential surface thereof; and 
 an outer pipe into which the inner pipe is inserted, 
 wherein the helical valley/ridge portion formed on the outer circumferential surface of the inner pipe is a multiple-helix helical valley/ridge portion, 
 the inner pipe includes an annular groove formed by reducing an outer diameter from one side of the multiple-helix helical valley/ridge portion, a smaller-diameter connecting portion formed by reducing an outer diameter from the other side of the multiple-helix helical valley/ridge portion, and a larger-diameter connecting portion extending from the annular groove, 
 the outer pipe includes a larger-diameter fixing portion and a smaller-diameter fixing portion, 
 the larger-diameter fixing portion includes a helical outer pipe valley/ridge portion formed so as to be threadedly engaged with at least one helical valley/ridge portion of the multiple-helix helical valley/ridge portion, and first and second through-holes formed adjacent to both ends of the helical outer pipe valley/ridge portion, 
 the smaller-diameter connecting portion of the inner pipe has an outer circumferential surface diameter smaller than a diameter of an imaginary cylinder defined by an inner circumferential surface of a ridge formed on an inner circumferential surface of the outer pipe, and 
 the outer pipe is configured so that the first through-hole of the larger-diameter fixing portion communicates with the annular groove of the inner pipe and the second through-hole of the larger-diameter fixing portion communicates with the smaller-diameter connecting portion of the inner pipe. 
 
     
     
       8. The dual pipe according to  claim 7 , wherein the multiple-helix helical valley/ridge portion of the inner pipe is formed by pressing the outer circumferential surface of the inner pipe, and
 the helical outer pipe valley/ridge portion formed in the larger-diameter fixing portion of the outer pipe is formed by pressing an outer circumferential surface of the larger-diameter fixing portion of the outer pipe.